Doesn't matter if Smapras had a defensive or offensive backhand, he still won 14 gs, plus Federer probably slices 80% of his backhands. (recently with Annacone, he is slicing less)

How many Slams have Almagro and Wawrinka won?

1 handed BH is a stroke which is great when mastered. It has taken me years to get my one hander to be good enough at the 4.0 singles level to be handle high and top-spin balls without slicing, plus I also use a 2 hander when the ball is too fast for me, like a deep quick return to my serve. The times when I use the 2 hander by instinct has taught me the disadvantages of the 1 hander - longer time to setup, body turning sideways, vision not continuously focused on the front. It looks elegant may not be good enough reason to keep it if you are a kid. Me, at my age, cannot learn a 2 hander, except in the reflexive cases. For a kid, sky is the limit.

Thank you all for the constructive comments. She used to use 2hbh, and hit super hard as well. then she wanted to use ohbh due to her sister using it. actually i am debating if i should switch her back hand as well.

On 1hbh, she should close her stance more and generate arm swing speed from the pulling out and opening of the right shoulder while the left arm and shoulder anchoring the other side for balance. Currently the swing is too much pushing toward the target not generated full swing speed. When pulled from the shoulder with relaxed arm and firm wrist control, racquet head speed should increase (for that contact moment) quite a bit and can generate more topspin as well for better control.

Is she an excellent ball-striker? You can have a one-hander today and succeed if you are an exceptional ball-striker. If not it will be attacked and picked-on. She will also need a good serve and strong approach/volley game to stay offensive.

I would say she needs to work on playing closer to the baseline and taking the ball earlier. Regarding 1hbh vs 2hbh it depends what kind of player you think she will become. If she shows any disposition to play all-court game (and this clip does not prove that) then you can work on her backhand slice, volleys and transition game. Every successful junior girl with 1hbh that I saw had a relatively weak bh drive but a killer slice that they used to chip and charge or to pull their opponent to the net at will. They also went to the net at first chance and/or ran around their backhand a lot, they could move very well in all directions. Usually these players would do anything to escape getting involved into long baseline rallies that the majority of their opponents prefers. If you do not see your girl having these special talents to play this non-standard game then you will be much better off switching her back to 2hbh asap.
It is a pleasure to watch Mayo Hibi play but she lost to Taylor today and I suspect that she had big problems returning her serve with 1hbh. Maybe somebody who saw the match can comment?

Thank you all for the constructive comments. She used to use 2hbh, and hit super hard as well. then she wanted to use ohbh due to her sister using it. actually i am debating if i should switch her back hand as well.

I'd say stay with the 2hbh for those big drives,high balls,and most service returns .. and perfect that 1hbh slice,also using it for the volleys ...

Looking at the video I was thinking she was an OK but nothing special ~14 yr old. Finding out that she is 11 and she has years to improve shows that she could be pretty good. I also picked up on the weak backhand, but more the movement. It looks like she doesn't anticipate and move to the backhand side well. Also, with a one-handed backhand, even though there is more reach, movement is more important. The relationship of the body to the ball is more important and more exacting. Her contact point is late - she needs to get behind the ball and get her weight into it. Her serve looks pretty good for her age. Fundamentals on forehand and backhand could be improved, but she is only 11.

The backhand needs some work. She is hitting the ball too close to her body. She is not attacking the ball. If she is allowed to continue to hit her backhand this way it will become a defensive (pusher) type shot. I think she is too young to settle for that.
Fundamentals need to be revisited. Grip, take back, point of contact, and follow through. The more she plays with her type of swing the harder it is going to be to change the swing.
Good footwork is needed on the 1 handed back hand as well.
She is often stepping sideways or backwards to the ball. She should be cutting the angle off and and getting the right shoulder turned with ease.

Could you give me details? or give me the time on the clip? or some other video to demo? appreciate.

If you go to youtube there is a ton of free stuff to look at for the one handed back hand fundamentals. I would take a look at a bunch of them because there are quite a few different ways to hit a great one handed back hand. Go with the one that seems more natural for your daughters physical abilities.
Here is a website that someone sent to me from the stringforum. OnlineTennisInstruction.com. There are a lot of other good online tennis instruction sites too.

You can't flick your wrist like racquetball. You have to set that front-foot and then really plow through with a firm wrist and the front shoulder is a brake. The racquet face needs to just be closed over the whole time.

Freeze it at :21. She's falling to the side and then simply doing a wrist flick. There's a nice big take-back but it's not being used. She opens up before hitting so the shoulder-brake is just gone.

Ok, at 2:05, she sets up perfectly and the contact is mostly wrist. The arm needs to unfold over the ball and the force of the swing should bring her arm around. Right now, she just seems to tacking on the the follow-through.

Compare that to the FH where she is swinging with such force that the follow through is necessary for deceleration.

She is just absolutely smothering the ball right in her wheelhouse. The shoulder and front foot are planted. The wrist does not flick through. It naturally comes over in the deceleration. And she doesn't follow through "forward", she follows-through around her body because of the force of the swing.

As far as the slices, that's easy to fix. Don't simply chop under a ball. The path of the swing should be saucer shaped. i.e. with a slight upswing at the end so you are really going THROUGH the ball, not cutting at the bottom. That will also keep the ball down.

EDIT: Freeze the 2nd video at 4:11. Setting up with a nice "base". 4:12 Base gone. Finish the shot. Stay in there.

Henin's foot work is rock solid, getting herself into a position to make an easy shot. She knows exactly where she needs to be to strike the ball with confidence. Beautiful motion. One of my favorites.

Her secret was the extreme Eastern grip on the BH and an even balanced frame. That is how she got her power. Both are not advisable because they can cause arm problems. I would be careful about telling girls to follow her example.

Her secret was the extreme Eastern grip on the BH and an even balanced frame. That is how she got her power. Both are not advisable because they can cause arm problems. I would be careful about telling girls to follow her example.

That is why I suggested doing some research on the one handed backhand and go with what is most natural
I want to serve like Sampras but....